The objectives of our research in reproductive physiology are to determine: 1) the neural and endocrine factors which are implanted in the transition of the anestrous ewe to first heat by analyzing the capacity and sensitivity of the various endocrine and neural tissues of the gonadal-pituitary axis in anestrous and cycling ewes; 2) whether alterations in gonadotorpin and prolactin levels occur in male odor- stimulated responses in female mice, and whether the changes are the same in estrus synchronization, pregnancy block, and advancement of puberty; 3) whether extracts can be prepared from isolated rat seminiferous tubules and interstitial tissue which are capable of selectively depressing FSH levels, and to identify the responsible factors in such extracts; 4) whether progonadotropic and gonadotropic activities can be separated from the antiogonadotropic activity of immunized ewe serum, and to identify the hormone-hormone or hormone-immunoglobulin interactions responsible for these effects; and 5) whether lower vertebrates possess 1 or 2 gonadotropins, and if 1 what its nature is. Objectives of other studies are: 1) to continue to explore the mode of action of MSH in promoting darkening of hair in agouti mice, trying to determine whether effects on color, tyrosinase activity, and pigment granule ultrastructure are interdependent; 2) to examine the relative contributions of catecholamines and MIF to the inhibitory control of MSH release in frogs and toads, a lizard and the rat; 3) to evaluate the contribution, if any, of an intracellular site of action of polypeptide hormones and catecholamines to their total biologic effect; 4) to analyze the changes in prolactin and GH in searching for the factors involved in the stimulation of growth of ruminants by diethylstilbestrol; and 5) to purify further the compound(s) responsible for the trout bladder-contracting activity of extracts of the urophysis.